The present invention relates to a screen cleaning and comminuting system for sewage, wastewater and the like.
The processing of sewage and wastewater involves high flow rates of sewage and wastewater debris through a channel in which the debris is comminuted. Typically, the comminution of sewage and wastewater debris can be achieved by using various different screening and shredding devices in combination, with such devices being positioned directly in the wastewater flow within the channel.
U.S. Pat. No. 5,490,922 discloses a sewage water installation that has a discharge basin in which is arranged a screening unit linked to a back-and-forth movable cleaning carriage. The mesh screen unit is depicted schematically and includes a plurality of parallel spaced bars forming the screen. A cleaning car, which moves back and forth, is allocated to the mesh screen. If the mesh screen is longer, several cleaning cars can be provided. A preferred cleaning car is provided with teeth designed to protrude between the bars of the screen so as to clean the spaces therebetween.
U.S. Pat. No. 2,672,985 discloses a transverse linear screen extending across an influent channel that intercepts all solids too large to pass therethrough. The screen consists of a plurality of parallel, U-shaped members, with the U-shaped portions extending towards the inflowing sewage, forming a series of slots in the screen. A comminuting unit is disposed in parallel spaced relationship and in close proximity with the screen surface to remove collected solid materials therefrom by means of a cutting cylinder having a rotatable shaft to which a plurality of cutting cylinders and combs are secured. As the comminuting unit travels back and forth along the width of a single linear screen by means of a direct drive motor in engagement with a rack device, the teeth project into the U-shaped portion of the slot members so as to remove solids intercepted by the screen.
In U.S. Pat. No. 5,833,152, a unitary comminuting system, adapted for wastewater channel use, is provided with devices, which include a single or dual semi-cylindrical-like sizing screen. Each screen has a circular rotating sweeping mechanism of interactive slotted comb bars or blades adapted to sweep and clear lodged or agglomerated solids adhering to the outer convex circumference surface of the screen. The screen is disposed in parallel spaced relationship with a twin-shaft comminuting device having two parallel shafts with teeth along the length thereof that rotate in opposite directions relative to one another. The unitary system of devices is positioned perpendicularly between the influent and effluent sides of the wastewater flow in a channel so that solids therein will encounter the convex surface of the semi-cylindrical like sizing screens or the twin shaft comminutor as the wastewater flows through the channel. Both the single or dual semi-cylindrical-like screen devices cause solids, which do not flow directly therethrough, to be cleared away from the outer convex surface of the sizing screen. The unitary system employs the separate rotating sweeping interactive blade mechanism into surrounding the wastewater flow, so as to cause and divert or direct the solids to flow toward or into the contiguous twin shaft comminuting device. This is aided by circulating wastewater currents generated in the wastewater flow near the entrance to the twin shaft comminutor. It is generated in part by the rotating sweeping interactive blades of the screening devices, whereupon the removed solids are channeled into the twin shaft shredder device along with the other wastewater and solids flow where they are reduced in particle size.
In U.S. Pat. No. 4,919,346, a moving mesh conveyor-screen allows flow to pass through, while it diverts the solids to an adjacent twin shaft grinder for reduction in a unitized system. The screen is, however, ineffective at transporting solids during low flow conditions, subject to plastering of solid debris against the mesh screen surface and breakage due to stretching caused by water pressure. In addition, the screen suffers from maintenance problems.
U.S. Pat. No. 5,505,388 is substantially identical to the ""346 patent with the exception that the mesh-screen is wrapped around a sprocket to form a rotating drum-like member. Again, the rotating screen acts to allow flow to pass through while diverting oversized solids to the adjacent grinder. The operation can be inefficient and maintenance prone, because unreduced solids can bypass the grinder and pass downstream not masticated and because there are gaps between the rotating screen and the cutters through which a percentage of the solids pass unreduced. Further, solids become embedded in the rotating mesh drum-like screen and eventually get back-flushed downstream unprocessed. Maintenance problems result from the entrapment of solids within the central portion of the drum-like screen, requiring frequent cleaning. Also, the screen wears due to abrasion against bottom grit in the channel, while solids accumulating within the unit during power outages often require the unit to be manually cleared of debris before it can be restarted. Only approximately one quarter of the screen area is workable, as the part closest to the channel walls cannot effectively transport the solids, and the part in the back of the drum is not active. This results in a reduction in liquid-handling capacity.
U.S. Pat. No. 5,061,380 discloses another grinder-diverting system. It utilizes multiple parallel shafts with substantially parallel disks mounted thereupon, which intermesh one with another. The disks all rotate in a direction towards a vertically disposed grinder mounted to one side. The system uses an excessive amount of disks, drives and seal components; and, thus, it is extremely difficult to maintain. Solids, such as wood, can become lodged within the disks and present a blockage condition requiring manual removal.
None of the prior art systems described above is output controlled by any filtering device to assure a high percentage of reduction. They also suffer from components being mounted in the flow, which are subject to failure, wear, inefficient operation, seal failure, mechanical drive failure, etc. Many of the systems are crudely constructed, as well as being difficult and costly to install.
Accordingly, from a review of the foregoing prior art, it can be readily appreciated that it is desirable to provide a comminution system which is simple and cost effective in construction and having low maintenance requirements. The system should also be durable, efficient and effective as a comminutor.
Therefore, it is an object of the invention to avoid the shortcomings and deficiencies of the prior art devices described above.
It is another object of the invention to provide a comminution and screening system for reducing particle sizes in high flow applications.
Further, it is still another object of the invention to provide an effective and efficient self-cleaning screen and grinder system that can handle very high flow rates of sewage with low power requirements, minimal system parts for greater reliability and with a higher level of solids processing.
In accordance with the present invention, there is provided a comminutor apparatus having a filtering screen member with an upstream side for collecting solids carried by an effluent stream. The comminutor apparatus further includes a twin shaft grinder for grinding solids contained in the effluent stream and for cleaning the filtering screen member of solids collected thereon. The comminutor apparatus also includes a mounting member in the form of a frame-like structure for mounting the twin shaft grinder at a spaced distance from the upstream side of the filtering screen member. Additionally, the comminutor apparatus includes a moving device in the form of a drive motor for moving the twin shaft grinder past the upstream side of the filtering screen member such that the twin shaft grinder is continuously spaced from the filtering screen member during the movement of the twin shaft grinder. One embodiment of the invention includes an auger screen assembly being placed in cooperation with the twin shaft grinders to remove solid matter passing through the twin shaft grinders.